1. Field of the Invention
The present invention relates to an apparatus for forming phosphor layers in cathode-ray tubes such as color cathode-ray tubes.
2. Description of the Prior Art
Phosphor layers in color cathode-ray tubes, e.g., stripe-type color phosphor layers comprising red, green, and blue phosphor stripes and black stripes (light absorbing layer) formed between the red, green, and blue phosphor stripes, are produced as follows: First, a photosensitive film of PVA (polyvinyl alcohol) is coated on the inner surface of the front panel of a cathode-ray tube. After the coated photosensitive film is dried, it is exposed to an ultraviolet radiation using color selecting electrode as an optical mask. The exposed photosensitive film is then developed by being washed with water, producing stripe-shaped resist layers corresponding in position to the respective colors. The entire panel surface including the resist layers is coated with a carbon slurry. The resist layers and the carbon layer thereon are then lifted off, providing carbon stripes, i.e., black stripes, in a given pattern. Then, the panel surface is coated with a green phosphor slurry. After the coated slurry is dried, it is exposed through the color selecting electrodes. The exposed slurry is developed, forming green phosphor stripes between the carbon stripes. Similarly, blue and red phosphor stripes are thereafter formed between the other carbon stripes. Subsequently, the stripes thus formed are coated with an intermediate film and then a metal backing layer of Al, thus producing a color phosphor layer.
The photosensitive film, the carbon slurry, and the phosphor slurries are poured, coated, discharged, dried, exposed, and developed by a phosphor layer forming apparatus.
FIG. 1 of the accompanying drawings fragmentarily shows a general phosphor layer forming apparatus. As shown in FIG. 1, the phosphor layer forming apparatus has an array of successive coating tables 1 for coating respective green, blue, and red phosphor films, and an array of successive exposure bases 2 corresponding respectively to the coating tables 1. Each of the coating tables 1 has a plurality of (e.g., twenty-four) radial panel supporting arms 4 mounted on a rotatable main shaft 3 on the coating table 1. Each of the arms 4 has on its distal end a clamp head 5 that is rotatable about its own axis and also angularly movable about another axis, for holding a cathode-ray tube panel. The coating table 1 is surrounded by a developing unit for developing a photosensitive film or slurry, a drying unit comprising a heater for drying a developed photosensitive film or slurry, a pouring unit for pouring a slurry or a photosensitive solution, a discharging unit for discharging the slurry or the photosensitive solution, and a drying unit comprising a heater for drying the photosensitive film or the slurry, the units being arranged along the circumference of the coating table 1. While the main shaft 3 makes one revolution, the cathode-ray tube panel held by each of the clamp heads 5 moves successively through the above units, which develop a photosensitive film or the slurry, dry the same, pour a slurry or a photosensitive solution, coat the panel with the slurry or the photosensitive solution while spinning the panel, discharge the slurry or the photosensitive solution, and dry the coated slurry or photosensitive solution.
In the above respective steps at the units, the panel 6, as shown in FIGS. 2A through 2E, is rotated about its own axis and also angularly moved about the other axis by the clamp head 5 (not shown in FIGS. 2A through 2E). In the developing step, the panel 6 is angularly moved about the other axis through 180.degree. until the inner surface of the panel faces downwardly and is rotated about its own axis at a speed of 30 rpm, as shown in FIG. 2A. In the drying step after the development, the panel 6 is angularly moved about the other axis through 105.degree. and rotated about its own axis at a speed of 100 rpm, as shown in FIG. 2B. In the slurry pouring step, the panel 6 is angularly moved about the other axis through an angle ranging from 14.degree. to 10.degree. and rotated about its own axis at a speed of 5 rpm, as shown in FIG. 2C. In the spin coating step and the slurry discharging steps, the panel 6 is angularly moved about the other axis through 105.degree. and rotated about its own axis at a speed of 170 rpm, as shown in FIG. 2D. In the slurry drying step, the panel 6 is angularly moved about the other axis through 105.degree. and rotated about its own axis at speeds of 8 and 30 rpm, as shown in FIG. 2E.
After a desired slurry or photosensitive film is coated on the panel on one of the coating tables 1, the panel is transferred to the downstream exposure base 2 for exposure to an ultraviolet radiation. After the panel is exposed, the panel is unloaded or transferred to the next coating table 1.
On each of the coating tables 1, the clamp head 5 is rotated about its own axis by a motor, and angularly moved about the other axis through varying angles by either a cam groove or a motor. FIG. 3 of the accompanying drawings shows a conventional cam plate 7 having a cam groove 8 for angularly moving the clamp head 5. When a cam roller associated with the clamp head 5 moves along the cam groove 8, the clamp head 5 is angularly moved through an angle that varies depending on the step.
In the event of a failure occurring in one of the steps, panels get jammed on one of the exposure bases 2 to the extent that no more panels can be loaded or transferred from the upstream coating table 1 to the exposure base 2. On the coating table 1, the clamp heads 5 with the panels held respectively thereby are turned again in the respective steps.
Under normal conditions, the clamp heads 5 are stably angularly moved by the mechanical arrangement including the cam. If the clamp heads 5 are caused to turn in the respective steps due to a failure, however, the coating film on the inner surface of the panel is excessively heated by the heater. All the panels that are carried by those clamp heads which are turned again become defective when excessively heated.
With the motor used to angularly move each of the clamp heads 5, when the clamp head 5 is caused to turn again due to a failure, the motor may be controlled to direct the inner surface of the panel upwardly so that it will not be excessively heated by the heater. However, because of a complex control system required to control the motor and also the reliability of electric components used, the time efficiency of the entire system remains lower than a certain level.